Insufficient self-shielding correction in VITAMIN-B6

Konno, Chikara  ; Ochiai, Kentaro; Onishi, Seiki

We carried out a simple benchmark calculation test with the multigroup cross-section library VITAMIN-B6 generated from ENDF/B-VI. The model of this test consisted of an iron sphere of 1 m in radius with an isotropic 20 MeV neutron source in the center. Neutron spectra in the sphere were calculated with the Sn code ANISN and VITAMIN-B6 or FENDL/MG-1.1. A calculation with MCNP and FENDL/MC-1.1 was carried out as a reference. The neutron spectra with ANISN and FENDL/MG-1.1 agreed with those with MCNP, while those with ANISN and VITAMIN-B6 were by at most 50% larger than those with MCNP. We examined VITAMIN-B6 in detail in order to investigate causes for the discrepancy. As the result, it was founded out that reasons of the discrepancy were the followings; (1) The smallest background cross section of Fe in VITAMIN-B6 is 1. (2) The weighting function used in generating VITAMIN-B6 is not adequate. VITAMIN-B6 should be revised for adequate self-shielding correction.